Tips when playing Trundle:

Use Subjugate to soften a powerful enemy tank or to create a target for your team to focus fire.

Chomp is good for lowering the physical damage of enemies; try to focus it on enemy physical damage dealers.

The story of Trundle:

Trundle is a hulking and devious troll with a particularly vicious streak, and there is nothing he cannot bludgeon into submission—not even the Freljord itself. Fiercely territorial, he chases down anyone foolish enough to enter his domain. Then, his massive club of True Ice at the ready, he chills his enemies to the bone and impales them with jagged, frozen pillars, laughing as they bleed out onto the tundra.